awk '{print $1}' metals.txt | sort | uniq | wc -l
grep -E '中国(香港|台北)?' metals.txt | sort -t"," -k5,5nr
sort -t"," -k3 -nr metals.txt | head -n 5 | awk '{print $1}'
sort -k2 -nr metals.txt | head -n 5 | awk '{sum+=$2} END {print sum}'
